Technical Field
Embodiments of the present invention relate to a semiconductor laser driver and an image forming apparatus incorporating the same.
Background Art
As known in the art, electrophotographic image forming apparatuses use a semiconductor laser driver to drive a semiconductor laser, and irradiate an evenly charged photoconductor with a laser beam that is modulated according to image data. By so doing, an electrostatic latent image is formed on the surface of the photoconductor. The image forming apparatuses apply developer such as toner to the photoconductor to develop the electrostatic latent image, and then transfer the developed toner image to a recording medium such as a sheet of paper. Accordingly, an image is formed.
In such electrophotographic image forming apparatuses, as known in the art, the mounted semiconductor laser driver is provided with an automatic power control (APC) circuit. The semiconductor laser driver uses the APC circuit to control an adjustment current to adjust a driving circuit for a laser beam source according to an adjustment value for adjusting the light quantity of laser beam source to drive the laser beam source with a desired light quantity. This series of processes is referred to as APC processes.
In the image forming apparatuses, the image quality deteriorates due to optical variations or variations in electrical charge on the photoconductor. In order to handle such a situation, a semiconductor laser driver performs shading correction to correct such optical variations or variations in electrical charge on the photoconductor. The term “optical variation” indicates that the laser beam emitted from a laser beam source to a surface to be exposed, with an even light quantity, becomes uneven in light quantity due to the characteristics of a deflection element or lens which are arranged in between the laser beam source to the surface to be exposed. As known in the art, the semiconductor laser driver performs shading correction mainly by controlling the driving current (switching current) on the image area.
In recent years, image forming apparatuses are provided with a laser-beam source where a plurality of laser-beam source units such as vertical-cavity surface-emitting lasers (VCSEL) are arranged in the main scanning direction and the sub-scanning direction.